The present invention relates to the field of percutaneous catheterization of blood vessels.
Many medical procedures require the percutaneous placement of a catheter into a vein or artery. Catheterization of this type is used for blood pressure monitoring, blood sampling, or administration of drugs and fluids, for example. Until now, such catheters have usually been inserted by the technique described by Seldinger (Acta Radiologica. 39 [1953], 368-376). The Seldinger technique makes use of a relatively small gauge introduction needle which allows entry into a vessel without a cutdown and with minimal trauma to the vessel and surrounding tissue. More specifically, the vessel is entered obliquely by introducing a small thin-wall percutaneous lancet beveled needle through the skin and into the blood vessel. A somewhat stiff, but flexible, wire guide is then inserted through the bore of the needle about 5 to 10 cm into the vessel. While holding the wire guide in place, the needle is withdrawn. The catheter, having a tapered tip, is then inserted by sliding it over the wire guide and, with a twisting motion, advancing it through the skin at the needle puncture site and into the vessel. Once the catheter is in place within the blood vessel, the wire guide is withdrawn.
Conventional wire guides as used in the above procedure are comprised of a tightly wound helical stainless steel wire coil. Such wire guides, to have sufficient rigidity to properly support and lead standard catheters, are typically constructed with a diameter of 0.035 inches (20 gauge). The smallest standard needle which will allow a 0.035 inch wire guide to pass through it is an 18 gauge needle (0.049 inch), and thus the 18 gauge needle has become the standard needle for use with the Seldinger Technique for percutaneous catheterization.
Because of the unavoidable tissue trauma that results from insertion of a lancet beveled needle, it is desirable that as small a needle as possible be used to effect the initial entry. The present invention involves an improved Seldinger technique which utilizes a novel catheterization apparatus which allows a smaller gauge needle, namely 22 gauge (0.028 inch dia.), to be used for percutaneous insertion of standard catheters and catheter introducing sheaths of up to at least French size 9 (0.118 inch dia.). For convenience, the word "catheter" will be used below to refer to both catheters and catheter introducing sheaths, as they are analogous structures with respect to the present invention.
The principles upon which the present invention is based can be described briefly, as follows. Wire guides in the range of 0.018 inches in diameter (26 gauge) are now available with sufficient stiffness to be used confidently for introducing a catheter in the French size 5 to 9 range. Wire guides of this type are available from Cook, Incorporated, 925 South Curry Pike, P.O. Box 489, Bloomington, Indiana 47402, sold as the Cor-Flex.TM. line of wire guides. To use such a small diameter wire guide with such relatively large catheters, it is necessary to provide the distal end of the catheter with a smooth diametrical transition from the wire guide to the full diameter of the catheter. This enables the catheter to be more easily inserted through the skin at the puncture site with a minimum of tissue trauma. One way of accomplishing this would be to provide the external diameter of the catheter with a long gradually tapered tip which narrows at its distal end to a diameter only slightly larger than the wire guide. Likewise, the internal lumen of the catheter would have an opening at the distal end with a diameter only slightly larger than the wire guide.
One disadvantage of the long tapered tip approach is that the distal opening would necessarily be very small, on the order of 0.018 inches, which would impair the performance of the catheter by restricting fluid flow therethrough. Furthermore, it is known that long tapers are not desirable once inside the vessel, since they are likely to erode or damage the vessel wall.
The above mentioned problems are overcome or alleviated by the present invention, one principle of which is the provision of a catheter having a removable cannula located over the wire guide but inside the catheter. The cannula has a tapered tip which extends through the distal opening of the catheter, providing a diametrical transition between the large distal opening of the catheter and the wire guide. The catheter and the cannula are inserted into the blood vessel in unison. Once the catheter is properly positioned within the blood vessel, the cannula can be withdrawn, leaving the catheter in place. Thus, a catheter can be inserted percutaneously into a blood vessel using a wire guide and introducer needle which are much smaller in diameter than the distal opening of the catheter. This ensures good flow characteristics for the catheter and a minimum of tissue trauma to the patient.